The present invention relates to combustion devices which are designed for the disposal of flare gases by the process of combustion, and more particularly but not by way of limitation, to an improved flare gas combustion apparatus for the smokeless burning of hydrocarbon gases and vapors.
There are many facilities, such as refineries, that must dispose of flare gases in a safe and effective manner as directed by both local and federal governmental regulations. Prior art devices to accomplish this usually include a flare stack having a flare tip disposed sufficiently high enough above the terrain to disperse the combusted gaseous products into the prevailing wind and limit the thermal radiation to safe levels. It is to be expected, especially in view of recent clean air laws and ordinances, that the combustion must be complete and smokeless to minimize environmental disturbance. It is also desirable to have such devices capable of handling quantities of gases in excess of normal discharge loads during temporary plant upsets. Further, it is usually desirable to have a purge reduction device and/or a flash back prevention device which protects the plant from any inner conduit combustion.
Prior art devices typically use steam or air as a smoke suppressant, and the flare tip must deliver steam and air in adequate quantities to promote rapid mixing of these suppressants and gases in the combustion zone at the upper end of the stack. The steam serves to break up the discharging flare gas and promote more complete combustion. There are numerous such prior art devices which have been designed to effect smokeless, flare tip combustion of flare gases.
For example, U.S. Pat. No. 2,779,399, issued to Zink and Reed, teaches a flare tip structure to combust flare gas comprising hydrocarbons and other flammable raw materials. A flare stack tube has a main gas flare tip mounted at its upper end, and a sleeve surrounds the upper end of the tube forming an annular space about the flare stack. The purpose of the annular space is to communicate air and steam into the burning flare gas discharging from the flare stack tip. Steam is sprayed into the burning mass of gas via a centrally disposed tubular member and a manifold surrounding the burning tip; thus steam and air are drawn into the flame mass.
U.S. Pat. No. 3,512,911, also issued to Zink and Reed, teaches the use of air and steam which is directed into the center of the flare tip to break up the flame by developing turbulence to mix the steam and air with the flare gas to promote smokeless burning.
U.S. Pat. No. 3,547,567, issued to Turpin, teaches a flare stack combustion tip which breaks up the main gas flow into plural flow segments. The flare tip is affixed to the top of a flare stack or to the top of a centrally disposed flare gas conduit, the tip having a plurality of gas conducting channels which serve as gas emission orifices through which the flare gas is discharged for burning. Steam and air are directed through a shroud which surrounds the flare tip.
U.S. Pat. No. 3,554,631, issued to Procter, teaches a flare stack tip which attaches to the upper end of a flare stack. Rows of air-inducing devices are disposed to drive steam and air into the tip to mix with the flare gas flowing up through the stack, with the air-inducing devices operating under the Coanda principle. Proctor's later patent, U.S. Pat. No. 3,914,093, teaches a further development in a Coanda inducing device.
While most of the prior art flare gas combustion devices, including those taught by the above mentioned patents, provided devices which achieved varying degrees of success, they were generally expensive to fabricate and/or to operate, and experienced high maintenance costs. Devices which served to break up the "log mass" of the flare gases (so called because of the large tubular mass discharge from most prior art flare stacks) involved devices having components subjected directly or indirectly to the intense heat of the flame by placing the operating components in or near the flame mass, resulting in early burn out of the components. High operating expense incurred by the use of steam in quantities sufficient to suppress large masses of flare gases often diminishes the value of otherwise well designed flare combustion devices.